Do we have to put the word "that" after the word "understand' to introduce a sentence

[tiantian888]

Do we have to put the word "that" after the word "understand' to introduce a sentence? Is it more concise without "that" in most cases?

Thank you for your kind help.

[BobK]

Do we have to put the word "that" after the word "understand' to introduce a sentencesubordinate clause? No
Is it more concise without "that" in most cases? Some people think it is, but it can also be less clear. Use your own judgement to decide whether to include it.

Thank you for your kind help.

(Some audible clue that signals 'here comes a subordinate clause' can be very useful when you're preparing some writing to be read out loud.)

b